Charged particle beam device

ABSTRACT

The scanning charged particle beam microscope according to the present application is characterized in that, in acquiring an image of the FOV (field of view), interspaced beam irradiation points are set, and then, a deflector is controlled so that a charged particle beam scan is performed faster when the charged particle beam irradiates a position on the sample between each of the irradiation points than when the charged particle beam irradiates a position on the sample corresponding to each of the irradiation points (a position on the sample corresponding to each pixel detecting a signal). This allows the effects from a micro-domain electrification occurring within the FOV to be mitigated or controlled.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/023,936, filed Mar. 22, 2016, which is a 371 of InternationalApplication No. PCT/JP2014/065407, filed Jun. 11, 2014, which claimspriority from Japanese Patent Application No. 2013-199130, filed Sep.26, 2013, the disclosures of which are expressly incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to a charged particle beam device,particularly, a charged particle beam device that generates image dataor signal waveform data by scanning a beam.

BACKGROUND ART

With minuteness of a semiconductor pattern, a slight shape differenceaffects an operation characteristic of a device and needs for shapemanagement increase. For this reason, in a scanning electron microscope(SEM) used for inspecting and measuring a semiconductor, highsensitivity and high precision are required increasingly. In the SEM,when an electron beam irradiates a sample, secondary electrons emittedfrom the sample are detected and a shape of a surface is observed. Atthis time, the detected secondary electrons have low energy and areaffected by electrification of the sample. Due to recent minuteness of apattern or a use of a low permittivity material such as low-k, effectsfrom the electrification become obvious and it may become difficult tocapture a signal of a place where management is necessary.

In this case, because the energy of the secondary electrons emitted atthe time of irradiation of the electron beam does not change, changingof the state of the electrification of the sample surface becomes asolution. A method of changing an irradiation current amount andimproving a detection rate of a foreign material is disclosed in PTL 1.In addition, a method of changing a scan interval of an electron beamaccording to electrification time constant of an observed sample andsuppressing electrification of a surface is disclosed in PTL 2. A methodof changing a scan speed of a partial area in a field of view (FOV) andcontrolling an electrification state distributed on a surface isdisclosed in PTL 3.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Laid-Open No. 2002-353279

PTL 2: Japanese Patent No. 4914180 (U.S. Pat. No. 7,763,852)

PTL 3: Japanese Patent No. 5341924 (WO02012/102301A)

SUMMARY OF INVENTION Technical Problem

As described in PTL 1 and PTL 2, the electrification of the surface iscontrolled by changing observation conditions such as the irradiationcurrent and the energy of the irradiated primary electron and aninterval (Y direction) between scan lines and a signal amount of anobservation place can be optimized. In an actual sample, effects fromthe electrification of a minute area are viewed due to minuteness orlamination of a plurality of materials and the effects from theelectrification of the minute area may be left in only optimizationbetween the scan lines.

In addition, a pre-dose method of scanning an inner area faster than anouter area in a scan area and reducing an electrification amount of theinner area relatively, when beam scan (pre-dose scan) for theelectrification is executed on the sample, is described in PTL 3.However, the effects from the electrification in the minute area may beleft.

Hereinafter, a charged particle beam device to realize mitigation ofeffects from electrification in a minute area or control thereof will bedescribed.

Solution to Problem

As an aspect for achieving the object, there is proposed a chargedparticle beam device, including: a charged particle source; a deflectorwhich scans a sample with a charged particle beam emitted from thecharged particle source; an image memory which stores signals obtainedby scan of the charged particle beam for the sample; and a controldevice which controls the deflector, wherein the control device controlsthe deflector so that scan of the charged particle beam betweenindividual pixels is performed faster when the charged particle beamirradiates a position on the sample corresponding to each pixel.

Further, as another aspect for achieving the object, there is proposed acharged particle beam device, including: a charged particle source; adeflector which scans a sample with a charged particle beam emitted fromthe charged particle source; an image memory which stores signalsobtained by scan of the charged particle beam for the sample; and acontrol device which controls the deflector, wherein, when at least oneof a scan speed and an irradiation point interval at the time of scan ofthe charged particle beam is set to at least two states, the controldevice evaluates signals obtained in each state and selects at least oneof the scan speed and the irradiation point interval where an evaluationresult satisfies a predetermined condition.

Advantageous Effects of Invention

According to the above configuration, mitigation of effects fromelectrification in a minute area in an FOV or control of theelectrification in the minute area can be performed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an outline of a scanning electronmicroscope.

FIG. 2 is a flowchart illustrating a process for setting observationconditions according to a region of interest (ROI).

FIG. 3 is a diagram illustrating an example of a screen displaying anevaluation result of an image quality of the ROI for each combination ofa scan speed and an interval of irradiation points.

FIG. 4 is a diagram illustrating irradiation order of beams when an FOVis divided in a block shape.

FIG. 5 is a diagram illustrating an example of a scan signal supplied toa deflector.

FIG. 6 is a diagram illustrating an example of a semiconductormeasurement system including the scanning electron microscope.

FIG. 7 is a diagram illustrating an example of a graphical userinterface (GUI) to set a region of interest (ROI) of an observationpattern.

FIG. 8 is a diagram illustrating an example of an image when avia/trench pattern is normally scanned and an image obtained when blockscan is performed.

FIG. 9 is a diagram illustrating an example of an image in which ameasurement target in the FOV is set as a low-speed scan area and theother area is set as a high-speed scan area.

FIG. 10 is a diagram illustrating an example of forming an image byperforming beam irradiation in the ROI.

DESCRIPTION OF EMBODIMENTS

In an embodiment to be described below, a charged particle beam devicein which a beam scan speed and an interval between irradiation points atthe time of scanning a beam are appropriately adjusted to mitigateeffects from electrification in a unit of a minute portion in an FOVwill be mainly described. In addition, a charged particle beam devicethat can fine an optimal condition of at least one of the scan speed andthe interval between the irradiation points will be described.

In the embodiment to be described below, a charged particle beam devicewhich includes an objective lens to focus a charged particle beamemitted from a charged particle source, a deflector to change a scanposition of the charged particle beam, a control device to control thescan deflector, a sample stage to mount a sample, and a detector todetect a charged particle emitted from the sample and in which aplurality of data are acquired by repetitively changing a scan speed andan interval of irradiation points of the charged particle beam andobservation conditions of a measurement portion are selected from thedata, as a condition setting operation for setting the observationconditions before a regular observation, will be described.

A signal amount or a contrast ratio of the measurement portion can beimproved by setting the observation conditions on the basis of detectedconditions while changing the scan speed and the interval of theirradiation points.

FIG. 1 illustrates a schematic diagram of a scanning electron microscope(SEM) to be a type of the charged particle beam device. An electron beam2 generated by an electron gun 1 is focused by condenser lenses 3 and isfinally focused on a sample 6 by objective lenses 5. An electron beamscan area of the sample is scanned with the electron beam 2 by adeflector 4. A primary electron is scanned two-dimensionally and isexcited in the sample by irradiation, a secondary electron 7 emittedfrom the sample is detected by a detector 8, and a signal of an electronis converted into an image, so that the sample is observed and measured.The SEM illustrated in FIG. 1 includes an image memory to store adetection signal for each pixel and the detection signal is stored inthe image memory.

When the sample is a dielectric, a two-dimensional electrificationdistribution is formed in a scan area (FOV) during SEM observation.Because electrons mainly detected by the SEM are secondary electronshaving a large emission amount and small energy (several eV), theelectrons are affected by slight electrification formed on a surface.For this reason, in the SEM observation of the sample to be electrified,an obtained image changes according to an electrification distributionformed at the time of irradiation. As parameters to determine theelectrification distribution of the surface, there are energy of theprimary electron affecting an emission amount of the secondary electron,a current amount, and scan order and a scan speed of electron beams.

The primary electron energy and the current amount affecting theelectrification of an irradiation place are main parameters of anobservation condition search. When the sample surface is a uniformmaterial, the emission amount of the secondary electron is also constantand electrification control is relatively easy. However, with recentcomplication of a device structure, a pattern is often formed bycombining various materials and it becomes difficult to execute theelectrification control by only the primary electron energy and thecurrent amount. Meanwhile, the scan order and the scan speed areparameters including an effect of mitigation of electrificationaccumulated by irradiation and the present inventors have recognizedthat optimization of the parameters are important for measurement orinspection, by an examination.

With minuteness of a semiconductor device, effects from theelectrification of the sample on an image appear notably. In the SEMaccording to the related art, scan of an electron beam is generallyperformed in one direction with XY. However, due to effects from theelectrification within the FOV, a detection signal amount of anobservation place may be small or a signal may be detected, but contrastwith a surrounding pattern may not be taken. For a pattern in which anaspect ratio (=depth/hole diameter (or groove width)) is large, such asa deep hole and a deep groove, a method of increasing a detection amountof the secondary electron using positive electrification is taken.However, an image of a hole bottom or a groove bottom may be distortedby a distribution of the positive electrification.

To suppress occurrence of such a phenomenon, it may be effective tocontrol an electrification distribution of the sample surface. However,a shape and a dimension of an observation pattern included in anirradiation area are not constant and a long time is necessary forsearching an optimal scan method. For a material to form a pattern, anelectrification characteristic may be different according to adifference of manufacturing processes. Observation may be easy in awafer of a certain process, but the observation may be difficult in adifferent process.

Hereinafter, a scan condition determination method of improving thedetection signal amount or the contrast ratio of the observation area bychanging the scan speed and the interval of the irradiation points ofthe electron beam according to the observation pattern will be describedusing the drawings. Particularly, in this embodiment, a method ofsearching conditions where the signal amount or the contrast ratio isoptimized by changing the two parameters of the scan speed and theinterval of the irradiation points will be described.

FIG. 2 illustrates a flowchart for setting the observation conditions.First, an irradiation area (FOV) at the time of observation is set suchthat an observation pattern is included. Here, an observationmagnification and an observation angle (angle of the FOV to anobservation pattern0 are designated. Next, an area (ROI) for measurement(management) is designated in the FOV.

Here, any one of a mean signal amount (brightness) of the ROI, contrastratio with a separately designated place, contrast to noise ratio (CNR)with a separately designated place, and a shrinkage amount of aseparately designated area is designated for an index for optimization.When the contrast ratio is designated, an area to calculate the ROI andthe contrast ratio is additionally designated. The CNR shows themagnitude of the contrast of the ROI to noise and a noise determinationarea is designated in addition to the area to calculate the contrastratio. When the shrinkage amount is designated as the index, an area todetermine the shrinkage amount and an allowable value of the shrinkageamount are designated. A shape may be deformed by damage due toirradiation of the electron beam, depending on materials, and anobservation condition search with small damage is enabled by setting theshrinkage amount as the index. The scan speed and the interval of theirradiation points are changed with respect to the designated FOV,according to predetermined conditions, and scan is performed. Here, thescan speed corresponds to a scan speed in the FOV and the interval ofthe irradiation points corresponds to a division number of each of an Xdirection and a Y direction in the FOV. When the division numberincreases, the interval of the irradiation points decreases. Forexample, in the case in which the FOV is scanned with 512×512 pixels, ifthe division number of each of X and Y is 512, the interval of theirradiation points becomes 1 (continuous). An index value (any one ofthe mean signal amount, the contrast ratio, the CNR, and the shrinkageamount) is extracted from an image obtained as a result of each scan.

The obtained result is represented by a two-dimensional map exemplifiedin a lower diagram of FIG. 3. In this example, an example of the case ofextracting measurement conditions for the via/trench pattern exemplifiedin an upper diagram of FIG. 3 will be described. In this example, anexample of the case in which the via bottom is set as the ROI to measurea radius of the via bottom as the measurement target and the signalamount (brightness) or the contrast (for example, a brightnessdifference with the other designation portion) of the correspondingportion is detected will be described. The via exemplified in the upperdiagram of FIG. 3 is configured by laminating an upper layer linepattern 301 on a lower layer pattern 302. Axes of the map are the scanspeed and the interval of the irradiation points and display indexvalues of the individual conditions. In addition, each box of the map isdisplayed at brightness according to the obtained signal amount orcontrast ratio. For example, when a color of the map is bright, thesignal amount or the contrast ratio is high. By performing such display,a combination of the appropriate scan conditions can be easily detected.

In addition, conditions in which an index value is largest (for example,boxes in which the brightness or the contrast is highest) can beautomatically set from the map. However, an operator may select acondition from the obtained map. The operator can display scan order ofthe selected conditions (numbers of pixels to be scanned or a change ofirradiation points by animation) and confirm the scan order. Observationconditions for the obtained scan speed and irradiation point intervalare stored in a hard disk or a memory of the device and measurement isexecuted by reading the stored observation conditions.

The observation conditions can be read even in image acquisition by arecipe and an observation under the same conditions is enabled bypositioning the observation pattern by addressing. According to thisembodiment, even in the ROI in which it is difficult to extract theshape or the material contrast, it can be determined whether there areoptimal observation conditions. For example, in a semiconductormanufacturing process, high-precision and effective process managementis enabled.

Next, a method of setting the scan order when the interval of theirradiation points is increased will be described below. The interval ofthe irradiation points can be set by dividing the FOV into M×N blocks inX and Y directions. Here, the division is executed in a pixel unit of animage. In addition to setting the division number from the pixel numberof the acquired image, the FOV and the pixel number of the acquiredimage may be set on the basis of the block size and the pixel number.

FIG. 4 illustrates an example of the case in which an image of 6×9pixels is divided into 3×3 blocks. Here, the case in which scan startsfrom an upper left block 1 with respect to the 3×3 blocks isillustrated. First, an upper left pixel “1” of the block 1 isirradiated. In each block, because the same place is irradiated, a blocksize is matched with the interval of the irradiation points. In eachblock, the pixel “1” is irradiated. Then, after returning to the block1, a lower right pixel “2” in the block is irradiated. Here, as areference to select the pixel “2”, a distance with the previouslyirradiated pixel “1” of each block is calculated and a pixel in whicheffects from the electrification are minimized is selected. Here, a nextirradiation block is the block 1. However, pixel selection in the blockevaluates an influence under a condition where a block exists in asurrounding portion (for example, a fifth block of FIG. 4). Effects froman irradiated pixel and a previously irradiated pixel are represented bythe following formula (1). When a plurality of materials exist in theFOV or shapes (heights) are different, a weight coefficient of theelectrification may be applied. Here, a distance with a (1, 1) pixel “1”of each block is calculated and a pixel in which the distance is largestis set as a next irradiation point.

$\begin{matrix}{{F\left( {i,j} \right)} = {\sum\limits_{k = 1}^{9}\frac{1}{{R\left( {\left( {1,1} \right)_{k} - \left( {i,j} \right)} \right)}^{2}}}} & (1)\end{matrix}$

After the pixel “1” of each block to be a second irradiation point isirradiated, a third irradiated pixel is calculated on the basis of thefollowing formula (2) . In addition to the distance with the previousirradiated pixel, a coefficient of mitigation by a time is applied. Thisis to distinguish influences of the electrification in the immediatelypreviously irradiated pixel “2” and the pixel “1” irradiated before thepixel “2”. Here, a mitigation coefficient t of the electrification canbe set by the operator. Likewise, a fourth irradiated pixel iscalculated by the following formula (3).

$\begin{matrix}{{F\left( {i,j} \right)} = {{\sum\limits_{k = 1}^{9}\frac{1}{{R\left( {\left( {3,2} \right)_{k} - \left( {i,j} \right)} \right)}^{2\;}}} + {t{\sum\limits_{k = 1}^{9}\frac{1}{{R\left( {\left( {1,1} \right)_{k} - \left( {i,j} \right)} \right)}^{2}}}}}} & (2) \\{{F\left( {i,j} \right)} = {{\sum\limits_{k = 1}^{9}{\frac{1}{{R\left( {\left( {2,2} \right)_{k} - \left( {i,j} \right)} \right)}^{2}}t{\sum\limits_{k = 1}^{9}\frac{1}{{R\left( {\left( {3,2} \right)_{k} - \left( {i,j} \right)} \right)}^{2}}}}} + {t^{2}{\sum\limits_{k = 1}^{9}\frac{1}{{R\left( {\left( {1,1} \right)_{k} - \left( {i,j} \right)} \right)}^{2}}}}}} & (3)\end{matrix}$

The above processing is executed on all pixels of each block and theirradiation order in the FOV is determined. When weighting of thematerial characteristic or the shape is not performed, the irradiationorder is determined by a pixel number of a block. Therefore, theirradiation order corresponding to the block size may be previouslytabulated.

<Scan Signal>

A scan signal when discontinuous irradiation illustrated in FIG. 4 isperformed is exemplified in FIG. 5. FIG. 5 illustrates transitions of anX-scan signal and a Y-scan signal when pixels from the pixel 1b “1” ofthe block 1 of FIG. 4 when a time t is set as a horizontal axis to apixel “1” of a block 4 are scanned with an electron beam (movementsbetween individual pixels are described as (a), (b), and (c)). In FIG.5, V shows a maximum deflection voltage in X and Y directions. In thisexample, because an example of adopting an electrostatic deflector isdescribed, a deflection signal is displayed with a voltage value.

An irradiation time of pixels is set as Δt and electrons emitted in theirradiation time of Δt are detected. An inclination α of a scan signalshows a scan speed and when the inclination is large, the movement speedof the electron beam is high. The movement between the pixels has theinclination α larger than the inclination in normal scan and when theinclination is large, the movement speed of the electron beam is high.Therefore, the number of electrons irradiated at the time of themovement between the pixels can be reduced. The movement speed may becalculated from the irradiation current amount and the interval(distance ΔL) of the irradiation points. In addition, a change of thescan time to be the parameter corresponds to a change of the pixelirradiation time Δt. By changing Δt and ΔL, an image is acquired.Irradiation of the electron beam based on a point is enabled by usingthe XY scan signals and an electrification state of the surface can becontrolled by a material and a structure of the sample.

As described using FIG. 5, the scan speed of the beam scan at the timeof the movement between the pixels is set to a high speed with respectto the beam scan when a signal is detected (sampled), so that effectsfrom the electrification by the beam scan can be mitigated while anecessary signal is secured. Particularly, when a plurality of pixelsare skipped and scanned, the same scan line orbit is scanned with a beamseveral times to obtain a signal of one frame. For this reason, thismethod of maximally suppressing the beam irradiation not used for signalacquisition is very effective.

According to the scan using the scan signal exemplified in FIG. 5, bothmitigation of accumulation of the electrification by irradiating theadjacent portion with the beam continuously and mitigation ofaccumulation of the electrification by scanning the same scan orbit withthe beam several times can be realized.

<Cooperation with Design Data>

A control device of the scanning electron microscope has a function ofcontrolling each configuration of the scanning electron microscope andforming an image on the basis of detected electrons or a function ofderiving a mean signal amount or a contrast ratio of a preset ROI, onthe basis of a strength distribution of the detected electrons. FIG. 6illustrates an example of a pattern measurement system including anoperation processing device 603.

In this system, a scanning electron microscope system including a SEMbody 601, a control device 602 of the SEM body, and the operationprocessing device 603 is included. In the operation processing device603, an operation processing unit 604 supplying a predetermined controlsignal to the control device 602 and executing signal processing of asignal obtained by the SEM body 601 and a memory 605 storing obtainedimage information or recipe information are embedded. In thisembodiment, the control device 602 and the operation processing device602 are described as separated elements, but may be an integratedcontrol device.

Electrons emitted from the sample by beam scan by the electrostaticdeflector 606 or electrons generated by a conversion electrode arecaptured by a detector 607 and are converted into a digital signal by anA/D converter embedded in the control device 602. Image processingaccording to an object is executed by image processing hardware such asa CPU, an ASIC, and an FPGA embedded in the operation processing device602.

A measurement condition setting unit setting measurement conditions suchas the scan conditions of the electrostatic deflector 606, on the basisof measurement conditions input by an input device 613, a measurementcondition setting unit 608 setting the measurement conditions such asscan conditions, and an image feature amount operation unit 609calculating brightness or contrast in the ROI input by the input device613 from obtained image data are embedded in the operation processingunit 604. In addition, a design data extraction unit 610 reading designdata from a design data storage medium 612 under conditions input by theinput device 613 and converting vector data into layout data accordingto necessity is embedded in the operation processing unit 604. Inaddition, a pattern measurement unit 611 measuring a dimension of apattern, on the basis of an acquired signal waveform, is embedded. Inthe pattern measurement unit 611, a line profile is formed on the basisof a detection signal and dimension measurement between peaks of aprofile is executed.

A GUI displaying an image or an inspection result to the operator isdisplayed on a display device provided in the input device 613 connectedto the operation processing device 603 via a network.

A part or an entire portion of the control and the process in theoperation processing device 603 are allocated to an electronic computermounted with a CPU and a memory in which images can be accumulated andthe process/control can be executed. In addition, the control device 602and the operation processing device 603 may be configured as oneoperation device. In addition, the input device 613 also functions as animaging recipe creation device that sets measurement conditionsincluding the coordinates of an electronic device necessary forinspection, types of patterns, and imaging conditions (an opticalcondition or a movement condition of a stage) as an imaging recipe. Inaddition, the input device 613 has a function of collating inputcoordinate information and information regarding the types of thepatterns with layer information of design data and identificationinformation of the patterns and reading necessary information from thedesign data storage medium 612.

The design data stored in the design data storage medium 612 isexpressed in a GDS format or an OASIS format and is stored in apredetermined format. In addition, software displaying the design datacan display a format thereof. If the design data can be handled asfigure data, a type thereof does not matter. In addition, the figuredata may be changed to segment image information showing an ideal shapeof a pattern formed on the basis of the design data and may be thesegment image information obtained by performing exposure simulation andexecuting deformation processing to approach an actual pattern.

In the measurement condition setting unit 608, appropriate scanconditions are set by the step exemplified in FIG. 2. For example, themagnitude of the FOV, a position (the coordinates) of the FOV, themagnitude of the ROI, and a position of the ROI are set to layout datain the vicinity of a measurement target pattern extracted by the designdata extraction unit 610, using the input device 613, so that operationconditions of the device are automatically set. More specifically, anFOV position for each combination of a plurality of scan speedconditions and a plurality of irradiation point interval conditions isdetermined. At this time, a pattern structure in the FOV is the same anda plurality of areas at different positions are selected and areregistered as the FOV.

In the design data extraction unit 610, the design data is read from thedesign data storage medium 612 according to the conditions input by theinput device 613 and the vector data is converted into the layout dataaccording to the necessity, so that setting of the FOV or the ROI on thelayout data is enabled.

In the measurement condition setting unit 608, the scan speed and theirradiation point interval are changed. In addition, the image featureamount operation unit 609 extracts signal information of the ROI fromthe acquired image and generates a display signal of the input device613. The image feature amount operation unit 609 derives the indexvalues (the mean detection signal amount and the contrast ratio with adesignation portion) of the ROI set previously for each scan condition,on the basis of the detection signal, and displays a map of the indexvalues to the scan speed and the irradiation point interval exemplifiedin FIG. 3 on a display screen of the input device 613.

The designation of the ROI is performed on the previously acquired image(or the layout data). The ROI is set by designating any two-dimensionalarea on the image. FIG. 7 is a diagram illustrating an example of a GUIscreen to set the operation conditions of the SEM. Particularly, asetting unit to set the operation conditions of the SEM when the scan isperformed to select the appropriate scan condition from the plurality ofscan conditions is provided in the GUI screen exemplified in FIG. 7. Aplurality of windows to set beam conditions are provided in a beamcondition setting window 701. In an example of FIG. 7, Location(coordinates), Pattern Type (type of a pattern), Vacc (accelerationvoltage of a beam), Number of Frames (number of integration frames), FOV(magnitude of the FOV), Probe Current (beam current), and Rotation Angle(scan direction) can be set.

In addition, a scan speed setting unit 702, a scan block setting unit703, and an image evaluation parameter selection unit 704 are providedon the GUI screen exemplified in FIG. 7. In the scan speed setting unit702, a plurality of scan speeds can be selected and in the measurementcondition setting unit 608, scan conditions are set according to thenumber of set scan speeds or a combination of the number of set scanspeeds and the irradiation point interval and are registered in thememory 605. In the scan block setting unit 703, the coordinates of anarea to be set as the ROI are set. In addition, although not illustratedin the drawings, a setting unit of the irradiation point intervalconditions may be provided and a desired irradiation point interval maybe selected. In addition, only the designated ROI can be irradiated bychecking a check box of Scan Area Definition. In addition, in the imageevaluation parameter setting unit 704, it is determined which parameteris used to evaluate the ROI to be evaluated. In the GUI screenexemplified in FIG. 7, two parameters of the contrast of the ROI to bemeasured and other ROI and the brightness of the ROI can be selected.The ROI can be set by a setting screen 705. A parameter for evaluatingthe ROI may be a resolution evaluation value such as sharpness in theROI. According to an object of the measurement or the inspection, otherimage evaluation parameter may be selected.

For example, as illustrated in FIG. 7, it is assumed that an observationtarget is a via in a trench. At this time, when a signal amount of abottom of the via needs to be increased, the bottom of the via isdesignated as the ROI by a cursor box. At this time, there is a contrastratio of the ROI and a surrounding portion or a mean signal amount(brightness) of the ROI as an optimization index. When the contrast isselected, an area B to compare the brightness is designated by theoperator using the cursor box. The index value is acquired by changing ascan speed and an irradiation interval (scan block). For the scan speedand the block number, necessary conditions are set by the operator. Aplurality of conditions can be set with the scan speed and the blocknumber.

As described above, effects from the electrification are suppressed byevaluating the parameters of the ROI for each of the scan speed and/orthe irradiation point interval and fining an appropriate scan conditionand high-precision measurement can be performed.

A specific example of changing the irradiation point interval andincreasing a signal amount of a specific portion will be describedbelow. FIG. 8 illustrates a simulation result obtained by observing avia-in-trench shape in which a via exists in a trench. Here, the ROI iscontrast of a shape in a via bottom. A pattern is irradiated with anelectron beam, electrons detected from a sample are counted for eachpixel, and a detection electron image is formed. In addition, in thesimulation, influences of the electrification by a primary electron anda secondary electron are considered.

In (a) of FIG. 5, a contour of a hole bottom formed in a space cannot bedetermined in scan (−X→+X and +Y→−Y) of a normal direction. Meanwhile,the FOV is divided into 4×4 blocks and electron beam irradiation isperformed.

In (b) of FIG. 5, the contour of the hole bottom can be determined andcontrast of the hole bottom to be the ROI increases. This shows that theelectrification of the surface is mitigated by changing the interval ofthe irradiation points and observation condition optimization accordingto an observation place is effective. In a structure illustrated in thisembodiment, a space and a line are configured using a dielectric and acharacteristic of the electrification is changed by a manufacturingprocess. In this case, the observation conditions are optimized in onlythe first in a wafer to perform observation, so that the same conditionscan be reflected in the following observation. In addition, a materialcharacteristic of the sample such as the mitigation of theelectrification can be predicted from the change in the scan speed orthe irradiation point interval.

Next, an example of changing the scan speed in the ROI and the otherarea will be described using the drawings. In the embodiment describedabove, as exemplified in (a) of FIG. 5, an example of controlling thedeflector so that the scan of the charged particle beam between theindividual pixels is performed faster than when position on a samplecorresponding to each pixel is irradiated with a charged particle beam(in the example of FIG. 5, a speed is zero) has been described. This isto realize both securing of a signal necessary for measurement andaccumulation of the electrification by performing the scan at a lowspeed (including a stop) to increase the irradiation amount of the beamin a place (portion corresponding to each pixel) to extract a signal andperforming the scan at a high speed to suppress the accumulation of theelectrification in the other place. Meanwhile, in a criticaldimension-SEM (CD-SEM) to measure a pattern width, information of anedge portion to measure the pattern width is very important, but theother portion is not so important. Therefore, a scan method of realizingboth high precision of the measurement and reduction of effects from theelectrification by scanning the ROI portion necessary for themeasurement at a low speed and scanning the other portion at a highspeed will be described hereinafter.

FIG. 9 illustrates an example of the case in which four hole patterns902 exist in an FOV 901. Here, when a diameter of an X direction of thehole pattern 902 is measured, it is necessary to increase S/N of atleast left and right edges of the hole pattern. Meanwhile, for the otherarea, a shape may be determined to some degree. From the viewpoint ofsuppressing the electrification in the FOV, non-irradiation of the beamis preferable.

Therefore, a method of realizing both suppression of the electrificationand high-precision measurement by setting an ROI 903 for a low-speedscan area (high-efficient secondary electron detection area), scanningthe area at a low speed, and scanning the other area at a high speed issuggested. The ROI 903 is selectively scanned at a low speed (an areaother the ROI 903 is scanned at a relatively high speed), so that theROI enabling the high-precision measurement can be inserted into animage schematically representing a measurement target pattern.

For the scan speed in the ROI, a condition where a height difference ofa bottom and a peak of a profile waveform becomes larger than apredetermined value (first threshold value) may be selected. Inaddition, a condition where the height difference of the bottom and thepeak is not more than a predetermined value (second threshold value) notto perform excessive beam irradiation on the ROI may be set.

According to this embodiment described above, an area where a number ofsignals need to be acquired is scanned at a low speed and the other areais scanned at a low speed, so that both high precision of desiredmeasurement or inspection and suppression of effects fromelectrification can be realized.

FIG. 10 illustrates an example of forming an image by irradiation ofonly an ROI of a sample. If magnification and a pixel number aredetermined after addressing of an observation pattern, an existence areaof the ROI can be determined. The operator applies constant likelihoodpreviously on the GUI and designates an irradiation area, so thatinformation of only the ROI is obtained. At this time, an image isoutput at the same magnification as normal whole surface scan, so thatmeasurement of the ROI can be performed. Such observation is effectivefor the sample in which the electrification or the shrinkage (damage) isnotable.

REFERENCE SIGNS LIST

-   1 electron source-   2 electron beam-   3 condenser lens-   4 deflector-   5 objective lens-   6 sample-   7 secondary electron-   8 detector

The invention claimed is:
 1. A charged particle beam device, comprising:a deflector which scans a sample with a charged particle beam emittedfrom a charged particle source; an image memory which stores signalsobtained by a scan of the charged particle beam for the sample; and acontrol device which controls the deflector, wherein the control devicecontrols the deflector so that scan for sequentially irradiating thecharged particle beam for generating an image at a sample positioncorresponding to each pixel of the image stored in the image memory isperformed so that an interval between individual pixels is changed,thereby generating a plurality of images corresponding to a changedinterval between the individual pixels, and thus determines a deflectioncondition of the deflector based on evaluation of the plurality ofimages.
 2. The charged particle beam device according to claim 1,wherein the control device controls the deflector so that scan of thecharged particle beam between each of sample positions to be irradiatedwith the charged particle beam for generating the image is performedfaster compared with when the charged particle beam irradiates each ofthe sample positions to be irradiated with the charged particle beam forgenerating the image.
 3. The charged particle beam device according toclaim 1, wherein the control device determines the deflection conditionbased on index values obtained from the plurality of images.
 4. Thecharged particle beam device according to claim 3, wherein the controldevice determines the deflection condition based on at least oneevaluation selected from signal amounts of the images, a contrast ratio,a contrast to noise ratio, or a shrinkage amount of a pattern.
 5. Thecharged particle beam device according to claim 1, wherein the controldevice generates the plurality of images by changing, for a scan regionin a predetermined range, an interval between individual samplepositions to be irradiated with the charged particle beam for generatingthe image.
 6. The charged particle beam device according to claim 1,wherein the control device divides the image into a plurality of blockscorresponding to an interval between the individual pixels, and controlsthe deflector so that the charged particle beam sequentially irradiatescorresponding positions in the divided blocks.
 7. The charged particlebeam device according to claim 6, wherein the control device changes theinterval between the individual pixels by changing sizes of the blocks.8. The charged particle beam device according to claim 1, wherein thecontrol device controls the deflector so that, when a region of interest(ROI) set in the image is scanned with the charged particle beam, scanof the charged particle beam is performed at such an irradiation pointinterval between the individual pixels becomes relatively smaller incomparison with that in a region outside the ROI.
 9. An image generatingmethod for generating an image using a signal obtained by scanning asample with a charged particle beam emitted from a charged particlesource, comprising: deflecting the charged particle beam so that scan ofthe charged particle beam for generating an image at a sample positioncorresponding to each pixel of the image is performed while an intervalbetween individual pixels is changed, thereby generating a plurality ofimages corresponding to the changed interval between the individualpixels, and thus determining a deflection condition for deflecting thecharged particle beam based on evaluation of the plurality of generatedimages.
 10. The image generating method according to claim 9, whereinscan of the charged particle beam between each of the sample positionsto be irradiated with the charged particle beam for generating the imageis performed faster compared with when the charged particle beamirradiates each of the sample positions to be irradiated with thecharged particle beam for generating the image.